Package org.apache.zookeeper.server.watch

Class WatchManagerOptimized

  • All Implemented Interfaces:
    IDeadWatcherListener, IWatchManager
    public class WatchManagerOptimized
extends Object
implements IWatchManager, IDeadWatcherListener
    Optimized in memory and time complexity, compared to WatchManager, both the memory consumption and time complexity improved a lot, but it cannot efficiently remove the watcher when the session or socket is closed, for majority use case this is not a problem. Changed made compared to WatchManager: - Use HashSet and BitSet to store the watchers to find a balance between memory usage and time complexity - Use ReadWriteLock instead of synchronized to reduce lock retention - Lazily clean up the closed watchers

    • Constructor Detail

      • WatchManagerOptimized

        public WatchManagerOptimized()

    • Method Detail

      • addWatch

        public boolean addWatch​(String path,
                        Watcher watcher)
        Description copied from interface: IWatchManager
        Add watch to specific path.
        Specified by:
        addWatch in interface IWatchManager
        Parameters:
        path - znode path
        watcher - watcher object reference
        Returns:
        true if the watcher added is not already present

      • containsWatcher

        public boolean containsWatcher​(String path,
                               Watcher watcher)
        Used in the OpCode.checkWatches, which is a read operation, since read and write requests are exclusively processed, we don't need to hold lock here. Different from addWatch this method doesn't mutate any state, so we don't need to hold read lock to avoid dead watcher (cnxn closed) being added to the watcher manager. It's possible that before we lazily clean up the dead watcher, this will return true, but since the cnxn is closed, the response will dropped as well, so it doesn't matter.
        Specified by:
        containsWatcher in interface IWatchManager
        Parameters:
        path - znode path
        watcher - watcher object reference
        Returns:
        true if the watcher exists, false otherwise

      • removeWatcher

        public boolean removeWatcher​(String path,
                             Watcher watcher)
        Description copied from interface: IWatchManager
        Removes the specified watcher for the given path.
        Specified by:
        removeWatcher in interface IWatchManager
        Parameters:
        path - znode path
        watcher - watcher object reference
        Returns:
        true if the watcher successfully removed, false otherwise

      • removeWatcher

        public void removeWatcher​(Watcher watcher)
        Description copied from interface: IWatchManager
        The entry to remove the watcher when the cnxn is closed.
        Specified by:
        removeWatcher in interface IWatchManager
        Parameters:
        watcher - watcher object reference

      • processDeadWatchers

        public void processDeadWatchers​(Set<Integer> deadWatchers)
        Entry for WatcherCleaner to remove dead watchers
        Specified by:
        processDeadWatchers in interface IDeadWatcherListener
        Parameters:
        deadWatchers - the watchers need to be removed

      • size

        public int size()
        Description copied from interface: IWatchManager
        Get the size of watchers.
        Specified by:
        size in interface IWatchManager
        Returns:
        the watchers number managed in this class.

      • getWatchesByPath

        public WatchesPathReport getWatchesByPath()
        Iterate through ConcurrentHashMap is 'safe', it will reflect the state of the map at the time iteration began, may miss update while iterating, given this is used in the commands to get a general idea of the watches state, we don't care about missing some update.
        Specified by:
        getWatchesByPath in interface IWatchManager
        Returns:
        watch report
        See Also:
        WatchesPathReport

      • getWatcher2PathesMap

        public Map<Watcher,​Set<String>> getWatcher2PathesMap()
        May cause OOM if there are lots of watches, might better to forbid it in this class.

      • dumpWatches

        public void dumpWatches​(PrintWriter pwriter,
                        boolean byPath)
        Description copied from interface: IWatchManager
        String representation of watches. Warning, may be large!
        Specified by:
        dumpWatches in interface IWatchManager
        Parameters:
        pwriter - the writer to dump the watches
        byPath - iff true output watches by paths, otw output watches by connection